64 SPECTRA OF VOLATILIZED METALS. PARTI. 



The heat of the electric spark volatilizes the metals 

 which form the points of the conducting wires ; and all 

 volatilized metals give characteristic spectra, both 

 visible and chemical. The visible part differs from that 

 of the solar spectrum in being crossed by bright lines 

 instead of dark ones ; but the number, intensity, and 

 position of both the visible and invisible lines change 

 with each metal. The changes in the invisible part 

 under consideration may be readily observed by throw- 

 ing the spectra either on a fluorescent or collodion 

 plate. For example : in the spectrum from the spark 

 between thallium points thrown on the latter, Dr. Miller 

 found that there were two strong groups of lines in the 

 least refrangible part of the spectrum ; at a little distance 

 from these there were three groups, the two first less 

 intense than the third ; several rows of feeble dots fol- 

 lowed, and the chemical spectrum terminated rather 

 abruptly with four nearly equidistant groups. This 

 spectrum bears a resemblance to those of zinc and 

 cadmium, less strongly to that of lead. Dr. Miller 

 found that the photographic spectra of iron, cobalt, and 

 nickel, also have a strong analogy, but that the metals 

 arsenic, antimony, and tin showed as great a difference 

 in the invisible as in the visible part of their spectrum. 



The fluorescent spectra of seventeen metals were 

 examined by Professor Stokes of Cambridge ; several of 

 them showed luminous lines of extraordinary strength, 

 especially zinc, cadmium, magnesium, aluminium, and 

 lead, which in a spectrum not generally remarkable 

 contains one line surpassing perhaps all other metals in 

 brilliancy. Some other metals exhibit in certain parts 

 of their spectra lines that are -both bright and numerous ; 

 on the whole some parts of the spectra are strong and 

 tolerably continuous, while in others they are weak. 

 This grouping of the lines is most remarkable in copper, 

 nickel, cobalt, iron, and tin. Of all the metals examined, 



